ENVIEONMENT 



99 



clouds gather more easily perhaps than at any other point in Arizona. 

 The summer rains, especially near these mountains, are intense and 

 local and are likely to destroy any correlation. 



Arizona-California rain record — There is a further important 

 advantage in using only the winter rainfall, namely, that such pre- 

 cipitation is essentially alike in Arizona and California. Since the 

 coastal region has practically no summer rain to complicate the situ- 

 ation, the trees of Arizona become admirable recorders of California 

 rainfall. In fact, it seems probable that these Arizona trees give a 

 better record of California rainfall than do the California trees, so far 



Flagstaff 



Nov.!' 



n*Ufl:Summer [^ Va/X W^V^ A W 



Flagstaf) 

 preci 



1850 1860 1870 1880 1890 1900 1910 1920 



Fig. 8 — Flagstaff rainfall and tree-growth, with comparison curves; the tree-growth shows 

 close relation to winter precipitation 



discovered, though it is possible that very carefully selected sequoias 

 will be found to give good records. This similarity in rainfall appears 

 in figure 8, where the Flagstaff, Prescott, San Diego, San Francisco, 

 and Mount Wilson rainfall curves are reproduced. From a meteoro- 

 logical point of view the similarity is not surprising, for the winter 

 storms of northern Arizona cover very large areas and come from the 

 coast with very trifling modification, giving precipitation in Arizona 

 about one day later than in California. 



Cibecue drought record — Figure 9 shows the record of a single 

 tree, J-3, as measured by the auto-plot method. It shows the droughts 

 between 1870 and 1905 in a striking manner. 



